The present invention relates generally to full duplex wireless communication, and more specifically to transmission and reception of information in the same frequency channel at the same time.
Prior art wireless networks such as 802.11a/b/g/n were designed for half duplex radios which limit the efficiency of bandwidth utilization and throughput, and increase the complexity of networking protocols. To achieve full duplex wireless communication, prior art wireless networks generally use separate frequency channels for transmitting and receiving, which increases the bandwidth requirement and reduces bandwidth efficiency.
Full duplex wireless networking capable of transmitting and receiving at the same time over the same frequency channel is highly desired because of its many advantages at both the physical layer and the MAC layer. An attempt was made to do so, as discussed in Jung Il Choic, Mayank Jain, Kaman Srinivasan, Philip Levis, Sachin Katti, “Achieving Single Channel, Full Duplex Wireless Communication,” Proceedings of the Sixteenth Annual International Conference on Mobile Computing and Networking, (MobiCom '10), (Sep. 20-24, 2010), the disclosure of which is incorporated by reference. In the attempt, use was made of a combination of an RF noise cancellation chip QHx220 by Quellan, antenna cancellation by positioning two antennas with half-wavelength distance difference, and prior art digital interference cancellation, but failed to achieve acceptable results. Two possible reasons for this failure include that the QHx220 chip's design is based on phase-shifting and attenuating a sample of the transmitted signal to cancel out the transmitted signal at the receiving antenna. It is basically a linear vector modulator. The QHx220 noise canceller chip has an input pin that is connected to the transmitter's output to sample the transmitted RF analog signal. It shifts the phase and changes the amplitudes of the sampled signal to minimize the transmitted signal component in the received signal at the receiving antenna. The design principle of the QHx220 chip therefore limits its application to narrow band signals because it is difficult to achieve π shift for all frequency components in a wide band signal. In addition, by positioning two transmitting antennas whose distances to the receiving antenna having a difference of half-wavelength λ/2 can only effectively cancel out signals at the center frequency with the wavelength λ.